521 had the lines on top of the frame where wet dirt collects and rots them out. The 620 are on the inside of the frame and aren't so bad.

Buy a flaring tool and a few feet of pre-made brake line and a couple of fittings... they don't have to be metric but they have to be all the same. I did this on my old Cutlass. It's impossible to make a perfect length splice so I made a small loop that can be opened up or closed to fit the cut out section.

My 710 FSM shows the brake line pressure without the booster. It's a 3/4" master and 130 pounds on the pedal produce just over 1,000 PSI of line pressure. If you weigh 200 pounds and stand on one leg that's what 200 pounds feels like. Fuck me in a panic I've lifted my ass clear of the seat and almost tore the steering column up out of the floor so I wouldn't doubt that 350-400 lb. or more is possible if suitably motivated to save your life. Lord knows what the line pressure might be!!!! 350 in is 2,600+ line pressure.

You might be able to buy a new SAE brake line that is long enough at the parts store or buy two SAE lines and a adapter piece to put them together to make one long line, this is likely what I would do if your not comfortable making your own brake lines, it really is not that hard to fix the brake line, the hard part is bleeding the line for most people.

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The 521's brake lines are SAE....3/16" line with 3/8x24 threads on the fittings. If you buy pre-made lines that are a bit long, you can typically put a loop or bends in the line to take up the excess. Doing that will eliminate having to flare any ends on. But, if you get a flaring tool, you can custom fit the lines to your truck. Are you still running drums?

If you don't know how to flare the lines, this vid will give you an idea on flaring and bending.

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I had someone hit me in the right front and damage my fender/front sheet metal/valance/bumper, I removed the fender, pounded it out, straightened out the sheet metal below the grill, pounded out the valance and put it back together, the bumper was a bitch, I didn't have a good extra, so I pounded on that for a while also, but when I put it on it looked bent at the inner mount bolts, I even had to straighten the bumper mount brackets, so I modified some 320 bumper over riders to fit the 320 bumper and it looks pretty good.

As much as I would like to make a double cab 521 I really don't need another project, I have too many Datsun trucks now, thanks for the offer but no thanks.

It really don't look that bad, you should fix it, I am positive you could sell it.

i turn the nipple The whole octagon block that it hooks up to turns loosing up from the cylinder so it just squirts out the side where it’s flush mounted to the cylinder when I bled the brake.I can remove it BPBlaster it and see it I can see if I can separate it then remove the struck bled nipple

i got Bap Geon boxed new front wheel cylinders but I remember in there was a issue getting these from rock auto and was missing the bled screws or the Y block.I think it wa Daniel or Wayno maybe Mklotz that mentioned this .You open the box and like are missing something which you have to get at the dealer.otherwise I would have ordered from the dealer situation.

but The front wheel cylinders do work it just the back sides that have issues

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I do not know if this will work in every situation, but even if they send you a metric brake cylinder you can use the SAE bleeder fitting/housing on the metric brake cylinder using the metric banjo bolt, all the means is you don't use the new part that comes with the brake cylinder, the banjo bolt is the same size SAE or Metric threads, but your using a metric brake cylinder.

The banjo bolt going thru these bleeder housings don't matter, metric or SAE makes no difference, you just need the banjo bolt to match the brake cylinder your using, the rest you can leave stock, I have done this myself but I don't remember all the specifics anymore.

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FYI - On my old 521 back in the day (late 70's), one of my kingpins broke on the Long Beach Freeway...I muscled if off the road. It turned-out that the Zirk fitting for it was never drilled-out all the way from the factory and it never got any grease.....